This invention relates to a pulse/direct current transmitting circuit used in key telephone systems.
A telephone system adapted to transmit both pulse data and DC power generally comprises a main operating unit and a plurality of key telephone sets connected to the main unit and respectively containing a central processing unit (hereinafter referred to as "CPU"). Further, the key telephone system requires, in addition to lines necessary for transmission of voice signals for speech, lines for inter-CPU data transmission and for power supply to the respective telephone sets. Since the system becomes complicated when the data transmission lines and DC power supply lines are provided separately, there has been used a circuit which generally employs the same lines for transmitting both data-transmitting pulses and power-supplying direct current, which is referred to as a pulse/direct current transmitting circuit.